1. Field of the Invention
This invention relates to a unique protection circuit for preventing a loss or change in the contents of an electronic memory system (e.g. a microprocessor controlled electronic pin ball game), as a result of undesirable line transients or power interruptions.
2. Prior Art
As is known to those skilled in the art, during the existence of power line interruptions or transient conditions, there may be a high occurrence of data loss or undesirable modification of stored data in an electronic memory circuit. One such electronic memory circuit which is adversely effected by power line interruptions is that utilized in a system, such as, for example, a micropressor controlled electronic pin ball game, wherein accounting data relating to bookkeeping and other credit information is stored and maintained. Power line interruptions may occur as a result of a power cut off, loading down the power supply with other utilization devices that consume large amounts of power, toggeling the power line, etc.
A conventional technique for protecting a low power semiconductor memory circuit from a loss of stored contents is a simple auxiliary battery backup arrangement that is integrated with the memory to maintain memory data integrity during power interruption. However, a major problem in this prior art scheme occurs during the transition from the line power supply to the auxiliary battery back up supply. During this transition period, the system d.c. power supply is in an out of tolerance condition (i.e. a condition wherein the available voltage deviates from the acceptable operating voltage level) which in turn causes a loss of control within the system microprocessor. As a result of this loss of control or uncertainty state, the microprocessor randomly produces control signals to undesirably write or to change the contents of the semiconductive memory. A loss or change of data stored in the semiconductive memory could result in loss of financial records and the corresponding profits relating thereto to the pin ball game operator.